“SAT” may be the most anxiety-inducing acronym in the high school student’s vocabulary. Changes to the test in 2005 have left college hopefuls with an even greater need to be prepared and have helped spawn sites offering practice tests, customized tutorials, essay tips, and promises of higher scores.

These sites cost anywhere from nothing for unlimited use to $500 for four months. Is it worth paying that much? Consumer Reports WebWatch, which investigates Internet credibility, tested 10 SAT prep sites last summer, when many students would prep for a retest: Barron’s, Boston Test Prep, the College Board, Kaplan, Number2.com, Online Test Prep, Peterson’s, PrepMe, Princeton Review, and SAT Secrets. Testers were 20 high school juniors who had taken the SAT once.

What we found. Testers thought Number2.com, a free site with no time limit, was as helpful as Kaplan and Princeton Review (not affiliated with the university), which charge $399 for limited-time access.

However, privacy protection and errors--from typos to repeated answers--were cause for concern on some sites. Students may need to choose opt-out boxes when registering or they could open themselves up to college-related promotional e-mail. Testers also found technical glitches when using browsers other than recent versions of Microsoft Internet Explorer.

How to choose. To save money, consider using Number2.com or downloading free practice tests at www.collegeboard.com, and explore free SAT test classes and materials at your child’s school. Invest $20 in a book (good choices include “The Rocket Review Revolution,” by Adam Robinson, and books by Princeton Review and Kaplan). And whatever site you’re considering, call it before registering to ask about refund and privacy policies.